1. Field of the Invention
The present invention relates to an image forming apparatus for use in, for example, a copying machine, a printer, a facsimile and the like. More specifically, the present invention relates to an image forming apparatus provided with a developing device, wherein the developing device has a paddle and the paddle supplies developer while agitating the same.
2. Description of the Related Art
An image forming apparatus used for a copying machine, a printer, a facsimile, and a multi-function machine which includes at least two of these functions selectively exposes the surface of a uniformly charged photoreceptor drum according to image information to form a latent image, develops the formed electrostatic latent image to form a toner image, and transfers the toner image to printing paper to print an image. Subsequently, the toner image which is not yet fixed is fixed on the printing paper. A developer is stored in a developer container, and a paddle provided with blades extending in the radial direction supplies the developer to a developing sleeve while agitating the same to cause the developing sleeve to hold the developer. Then, by supplying the developer from the developing sleeve having the developer held thereon to the photoreceptor drum, a toner image, which is based on the electrostatic latent image, is formed on the surface of the photoreceptor drum.
The paddle is an elongated member since it requires at least a length equal to the length of the developing sleeve which corresponds to the width of the printing paper. It is difficult to obtain such an elongated paddle with a high degree of accuracy by metal machining, and the machining cost is expensive. Injection molding of the elongated paddle with resin or plastic requires a high die cost, and it is also difficult to eliminate molding distortion generated in the axial (longitudinal) direction.
Therefore, as shown in FIG. 11 and FIG. 12, there is known a paddle 900 which is axially divided into a plurality of components 901 and each component 901 is individually formed by injection molding (see, for example, Unexamined Japanese Patent Publication No. 2002-40768). The components 901 each include blades 902 extending between both end surfaces in the axial direction. For example, FIGS. 11 and 12 disclose an assembly of a paddle including discontinuous blades extending in the radial direction and shifted by 30° and a helical blade made by connecting the axially divided plurality of components.
However, as shown in FIG. 12, in the paddle 900 obtained by connecting the axially divided plurality of components 901, since there is a limit in dimensional accuracy of the injection molding or the like, spaces s are generated between the blades 902 provided on each component 901 of the paddle 900 and blades 902 adjacent thereto. Such spaces s degrade the accuracy of supplying the toner by the paddle 900, and cause defective image formation. For example, since the developer is not agitated at positions where the spaces s exist, the developer conglomerates and causes defective image formation. Since the developer is not scraped up at the positions where the spaces s exist and thus is not supplied to the developing sleeve, there may be portions on the surface of the developing sleeve where the developer is not supplied. In such a case, there is a problem such that the developer is not supplied to a portion of the surface of the photoreceptor drum which opposes the developing sleeve. Hence, the toner is not adhered to the corresponding portion and hence an image with a void is formed on the printing paper, so that defective image formation results. Since there are the spaces s between the blades 902 of the paddle 900, if there are portions where a sufficient required amount of the developer is not held on the surface of the developing sleeve, there may be a case in which an image having a density less than that of the desired level is formed on the printing paper, so that defective image formation results.